yesterday i did a 100% water change (it was well needed) on my 10 gallon tank. when i went to check on my betta in the tupperware container i was keeping him in i noticedhe wasnt there! after searching i saw him laying on my windowsill moving his gills so i quickly got him back in the water. he used to swim all over before but now he just chills on the ground in his tank, but why? is he still in shock or something? think he'll make it? i've had the little guy for about a month and i really like him! ill post pics of him and his home, also feel free to pick out names!
*pics looks dark due to black sand and a black background, i also have a green light so i hopefully wont get algae, again*

I would suggest to leave him alone and keep his tank dark. if you have any IALs that would be great in helpin him to recover. Most bettas are able to recover from being out of water soon, however keep an eye out in case his condition worsens. If his condition does happen to worse, slowly acclimatize him to a salt treatment. (1-3tsp/gal).
Also make sure to keep him warm.

thank you aokashi! but i have a question that mey sound a bit dumb: what are IALs?

Oh sorry! Indian almond leaves. Oak leaves that have naturally browned and fallen off, thoroughly washed and cleaned will also work. so will 100% rooibos tea. These release tannins which helps the betta recover.